Method and apparatus for conversion of hydrocarbon gases



Sept. 30, 1941.

H. c. scHu'rT METHOD ANDAPPARATUS FOR CONVERSION HYDROCARBON GASES FiledAug. 5, 1936 4@NHA NNN Patented Sept. 3l), 1941 ME'rnon AND ArramizrusFon coNvEnsroN or mmnocAaBoN GAsEs Hermann C. Schutt, North Tarrytown,lN. Y., as-

signor to The Pure il Company, Chicago, Ill., a corporation of OhioApplication August r5, 1936. Serial No. 94,386

3 Claims.

This invention relates to method and apparatus for convertingpredominantly or wholly saturated gases to liquid hydrocarbons boilingchiefly within the gasoline range. More particularly the inventioncontemplates conversion of saturated gases to liquids in a plurality ofsteps, in the rst of which the gases are cracked under conditions toconvert a substantial portion of the gases to oleiinic hydrocarbons andthe oleiins vare subsequently polymerized to liquids 4in one or moresteps.

In order to obtain high yields of motor fue distillate from unsaturatedhydrocarbon gases, it is essential that the conversion of gases does notexceed 50% per pass. As a result of the incomplete conversion,considerable quantities of gas must be recycled to the polymerizationzone in order to obtain suitable yields.

In accordance with my invention, I propose to subject the predominantlysaturated gases to cracking in a separate high temperature coil atelevated pressures and mix the cracked gases, leaving the coil at hightemperature, with preheated gases rich in oleflns so that the resultingmixture will be at a suitable polymerizing temperature andpressure',rand then to pass the mixture into a polymerizing zone. I havefound that at pressures of the order of 300-350 pounds per square inch.saturated gases can be cracked to yield a large amount of unsaturateswithout forming excessive amounts of liquid and/or tar.

The reaction products are then chilled with rich absorber oil and thepartially cooled products are fractionated to separate theliquerlableportions of the gas separated from the rich oil and reactionproducts. The liquefied gases are pumped to a preheating coil where thetemperature of the gas is raised sufllciently to give a suitablepolymerizing temperature when mixed with the cracked gases. Theuncondensed portion of the gas separated from the reaction products andrichabsorber oil may be recycled to the absorber and the undissolvedfraction of the gases eliminated from the system.

One of the objects of .my invention is to provide method and apparatusfor simultaneously cracking predominantly saturated gases Vandpolymerizing unsaturated gases with low fuel consumption. A

A further object of my invention is to subject saturated orpredominantly saturated hydrocarbons to high temperature for a shorttime to form methyl, vethyl and other alkyl radicals, and to immediatelysubject the activated gas in admixture with olefin-containing gases toconditions of polymerization and alkylation.

Another object of my invention is to provide method and apparatus forobtaining a high yield of liquid hydrocarbons boiling within the motorfuel range from predominantly saturated hydrocarbon gases.

A 4still further object of my invention is to` provide method andapparatus for converting predominantly saturated hydrocarbon gases toliquid hydrocarbons at elevated pressures and in a plurality of steps ina manner to avoid the necessity of compressing gas subsequent tocharging the gas to the cracking zone.

`Still another object of my invention is to crack saturated gases undersuch. super-atmospheric pressures as to avoid excessive formation ofliquid and tar and under pressures that are suit-` able forpolymerization of the cracked gases.

Other objects and advantages of my invention will.be apparent from thefollowing description considered in conjunction with the accompanyingdrawing, of which,

The figure is a diagrammatic elevational view of apparatus sultableforcarrying out the invention.

Referring to the drawing, numeral I indicates the line through whichpredominantly saturated or wholly saturated hydrocarbon gases arecharged to the system. The gases pass from the inlet of line I throughheat exchanger 3 and line 5 to heating and vcracking coil 'I located ina furnace 9. The heating coil I is preferably located in the radiantheat zoneof the furnace in order that the gases passing through may beheated to a suillciently high temperature. The

gasesmay be passed through the coil vfl at coil.

outlet pressures ranging from atmospheric to 400 pounds per square inchbut preferably at pressures of from 200-400 pounds per square inch andmay issue from the coil at temperatures ranging from l2001500 F. afterhaving been retained therein for a very short period of time. Thereaction products leave the heating coil 1 through the line Il and passinto the line I3, from which the gases may be passed into reaction coilsI5 by means of one or more of the lines I1 controlled by valves I9. Byproviding a plurality of lines I1, the products passing through thereaction coils may be subjected to any desirable period of reaction inthe coils I5.

For example, at higher temperatures and lowery C pressures, it may bedesirable to use a shorter reaction coil than would be desirable withlower temperatures and higher pressures. The reaction coils |5 may be ofthe same diameter as the heating coil 1 but are preferably of largerdiameter in order to provide a reduction i n` gas source later to bedescribed. In the arrester the products may be chilled to a temperaturebelowz 600 F. and preferably from 400500 F. From the arrester thechilled reaction products, to`

gather with the cooling liquid, pass through the line 23 controlled byvalve 24 into the lower portion of a fractlonatlng tower 25. Thepressure under which tower 25 is maintained will dependj on the pressureof the products issuing from the reaction coil. Vaporization of theproducts takesl 9| through the line 91 and either passed to stor` age orsubjected to-suitable refining. Gases and light fractions pass overheadfrom the stabilizer through the line 99 back to the upper portion of thefractionator 25.

The light vapors and gases which are not condensed in the fractionator25, pass over the top thereof through line |0| controlled by valve |02,heat exchanger |03, line |05, and condenser |01 where the gases arecooled to a temperature oi' 100 F. or less, and then into the gas andliquid separator |09. This separator |09 is preferably maintained at apressure of from atmospheric to 300 pounds per square inch. When tower25 is operated at low pressures, it will be necessary to insert aby-pass and compressor in line |05 in order to bringthe gases up tosuillcient pressure Y before entering the separator |09. A largeporplace in the fractionator, leaving as a residual,

tarry material inthe bottom thereof, which may be withdrawn through line21 controlled by valve 28 into a tar stripper 29 where the pressure maybe reduced. Any light or intermediate fractions condensed with the tarare revaporized in the` stripper 29 and passed overhead through line` 3|and condenser 33 into the tank 35. Residue may be withdrawn from thestripper through line 30; l The condensate isA withdrawn 'from tank 35 ithrough line 31 by means of pump 39, and a portionthereof recycledthrough the-line 4| to the `top ofthe stripper 29 to act as reflux. There- 3 mainder of the condensate withdrawn from the l tank 35 is pumpedthrough the linev 43 to the arrester`2| by means of pump 45 through line41 controlled by valves 49 and 5|. 1

l 'I'he vaporized portions in the fractionator 25 are partiallycondensed to separate the fraction 1 heavier than gasoline on the 4plate53 and to sepav rate naphtha and gasoline boiling point distili g lateson the plates 55 and 51. condensate from Q the plate 53 is withdrawnfrom the tower through the line 59 and a portion thereof may be recycledtothe bottom of the tower as reflux i through line 5| controlled byvalvev 53. The rel mainder of the condensate'withdrawn through line 59lmay be charged by means of the pump 55, either through line 51controlled by valve 59, line 10, lines 1| and 12 controlled by valves1|' and 12' respectively. heat exchangers 3 and 13, lines l l 14 and 15,heat exchanger 15, cooling coil 11 where the condensate is cooled to atemperature 1 of 100 F. or lower, and lines 19 into the upper L portionof an absorber tower 5|; or the valve 59 may be closed and thecondensate passed through line 52 and reboiler 53 back to line 10. Inre- 1 l boiler 53 the condensate passes in indirect heat 3 interchangewith the llighter distillate toimpart heat thereto. It will be apparentthat part of the l condensate may be by-passed around the reboiler and apart passed through it.

Naphtha or gasoline boiling point condensates are withdrawn from theplates 55 and 51 of the i fractionating tower 25 through either` line 54or 55 vgcontrolled'by valves 55 and 51 respectively, and

charged through line 55 to the upper portion of a stabilizing tower 9|.'I'he liquid from the stabilizer 9| passes through line 93 to thereboiler 53 gback to the stabilizer through line 95. Additional 1 heatis imparted to the condensate in the reboiler. sumcient to eliminate theunstable constituents l such as butylene, butane, propylene, etc. The:stabilized distillate is withdrawn from the tower tion of the heavierconstituents in the gas, such as butane, butylene, propylene, andpropane. will condense in the separator and are withdrawn therefromthrough line 0 by means of pump I. A portion of the condensate may bewithdrawn from the separator |09 by means of pump ||2 through line ||3,line ||4, and/or line ||5 as redux to the tower 25 ind/or the stabilizer9|. The uncondensed gases such as hydrogen,

methane, ethane, ethylene, and vsome propane and propylene, and a smallpart of the butane and butylene, are withdrawn from the top of thekseparator through the line I5 and returned to the lower portion of theabsorber 5|, wherev they pass in counter-current contact withcool oilintroduced into the upper -portion of the absorber throughline 19. Ifthe pressure on the gases leaving separator |09 is too low, a compressormay be connected in the line ||5 to bring the gases to suitable pressurefor the absorption step. However, the invention contemplates a processin which the gases leaving the separator I 09 are under suflicientpressure to avoid the necessity of compressing them. The absorber ispreferably maintained under a pressure of approximately -300 pounds 'persquare inch gauge. Any

gases which are not dissolved in the absorber pass over through the lineI1 controlled by valve ||9 and may be eliminated from the system. 'I'herich oil from the bottom 4of the absorber 5| is withdrawn through line|20 and is charged to the arrester 2| together with condensate from line43. Instead of pumping the rich oil from the absorber and the condensatefrom line 43 directly to the arrester, they ymay be by-passed throughline |3| and heat exchanger 15 where they assist in cooling the heavycondensate passing from the fractionator 25 -to the absorption tower 8|,and

-then passed back to line 41 through line |33; or

the stream may be split and only part passed through the exchanger. y

The liquefied gases in the separator |09 are withdrawn therefrom throughline ||0 by means of pump and pass through heat exchanger |03 where theyare heated by indirect exchange with vapors from fractionator 25,passing through line |2I, heat exchanger 13 where they are furtherheated by indirect exchange with heavy condensate from fractionator 25,and then passing through line |25, to the inlet of a heating coil |21preferably located Vin the convection heat zone of the furnace 9. Thegases are heated in the heating coil |21 to a coil outlet temperatureranging rfrom 5001000 F., and preferably from 600-950 F., under a coiloutlet pressure of from atmospheric to 400 pounds per square inch gauge.'I'he gases leave theheating coil |21 through the line |29 and Join thehot cracked gases 'from the line Il and are further heated thereby to atemperature of from 901200 F., and preferably to a temperature of10751175 F.

vI'he mixed gases then pass to the reaction coils i where conversion ofthe gases to liquids takes place. It will be apparent that the gas maybe fed to the reaction coils through any one of the several lines I1 orthe stream may be split and fed through any number of linessimultaneously. By providing several inlets to diierent portions of thereaction coil, the reaction time can be varied as desired to suit theparticular conditions of olefin concentration, temperature, and

pressureof the gases .entering the reactiqnzone.

At the temperatures and pressures t'o which'the gases are preferablysubjected in the reaction coil, a reaction time of from 5 to 30 secondsis suiiicient to accomplish the desired amount of conversion. i

Under the conditions of temperature and pressure at which my inventionis preferably carried out, a high octane motor fuel can be producedAwithout the use of excessive temperatures or pressures and with highyields. Although the system is particularly adapted to treatment ofnatural gas and low olefin-containing gases from high pressure crackingprocesses, hydrocarbon gases from any other source may be processed.

What I claim is:

1. The method which comprises subjecting hydrocarbon gases in a reactionzone to a condition of time, temperature and pressure suitable forconverting a substantial portion thereof to gasoline boilinghydrocarbons, fractionating the reaction products intoresidue,intermediate condensate, light condensate and gas, separating the gasinto a liquid and a gaseous portion, passing said liquid portion in heatinterchange with gases and intermediate condensate from thefractionating zone and thereafter charging said liquid portion to apreheating zone wherein it is heated to a temperature below the reactiontemperature, charging the gases leaving the preheating zone to saidreaction zone, passing intermediate condensate from the fractionatingvzone in heat interchange with the first mentioned gases prior tocharging to said reaction zone and thereafter charging said intermediatecondensate to an absorption zone, contacting said gaseous portionYcountercurrently with said intermediate con.

densate in said absorption zona-withdrawing rich condensate from saidabsorption zone and pass# ing it in heat interchange with'condensate'passing to said absorption zone and thereafter mixing said richcondensate with the aforesaid reaction products.

2. The method which comprises passing predominantly saturatedhydrocarbon gases successively through a heating and cracking zone and areaction zone, cooling the reaction products leaving the reaction zoneby direct contact with hydrocarbon liquid, fractionating the resultingmixture into residue, intermediate condensate,v

light condensate and gases, separating the gases into a liquid andgaseous portion, passing said liquid portion in heat interchange withgases and intermediate condensate from the fractionating zone andthereafter charging said liquid portion to a preheating zone whereinsaid 'portion is heated to a temperature below the desired reactiontemperature, mixing the gases leaving the preheating zone with gasesissuing from said heating and cracking zone in order to effect partialcooling of the latter, passing intermediate condensate from thefractionating zone in heat interchange with gases charged to saidheating and cracking zone and thereafter charging said intermediatecondensate to an absorption zone, contacting said gaseous portioncountercurrently with said intermediate condensate in an absorber,eliminating unabsorbed gases yfrom the system, withdrawing condensatecharged with gases from said absorber and passing it in -heatinterchange with condensate passing to said absorber,

and thereafter charging the condensate with absorbed gases to the outletof said reaction zone.

3. Apparatus ofthe character described comprising a heating coil and areaction means connected thereto by a connecting line, a second heatingcoil connected to said reaction means by said connecting line, afractionating means connected lto the outlet of said reaction means,means for separately withdrawing gasoline, condensate heavier thangasoline, and gases from said fractionatlng means, means for separatinggases leaving said fractionating means into gaseous and liquidfractions, means for recycling said liquid fraction to said secondheating coil, means for cooling said condensate, means for contactingsaidlcondensate with said gaseous fraction yunder super-atmosphericpressure, means for HERMANN C. SCHUTT.

